Voltage scaling has been used to reduce the power consumption of digital and analog circuits. It has been found that minimal energy may be achieved when the supply voltage is lowered to around or below the threshold voltage of transistors.
Future low power systems on chips (SOCs) are likely to include many components or cores operating at sub-threshold voltages to super-threshold voltages. The number of components or cores may be in hundreds. This requires hundreds to thousands of level shifters to be inserted between different power domains including the cores and the input/output (I/O). The level shifters are required to conduct wide ranging level shifting from sub-threshold up to IO voltage level with short delays and low energy consumption.